The present invention relates generally to improving emissions on a reciprocating engine and more particularly to an exhaust gas recirculation system for use with a reciprocating engine.
Exhaust gas recirculation (EGR) is a powerful tool for reducing NOx emissions substantially in combustion devices (e.g., reciprocating engines) by reducing flame temperature. There are various approaches for employing EGR on a 4-stroke engine.
One such approach is to route exhaust gas from the low-pressure side of a turbine through an EGR cooler to the inlet of an engine compressor. Unfortunately, this approach requires all of the exhaust to be both expanded and recompressed every time the gas is expanded and compressed, thereby resulting in efficiency losses. Furthermore, the EGR is routed through the intercoolers/aftercoolers, which are designed to cool clean air as opposed to the particulate-laden air that they are required to cool in this scenario. As a result, the particulates will foul the coolers, causing loss in their effectiveness.
Another EGR approach is to pump exhaust gas from the exhaust plenum into the intake manifold, downstream of the fresh air intercoolers. While fouling of the intercoolers is mitigated, this approach requires an additional pump to pump all of the EGR.
Another approach is to retain internal EGR in all cylinders of the engine. While this is a relatively simple approach, this method suffers from a shortcoming in that the EGR is not cooled and, thereby, less effective.
Accordingly, there is an ongoing need for improving emissions on reciprocating engines.